1. Field of the Invention
The invention relates to a label printer, and particularly to an arrangement for locking a cassette into a label printer and ejecting it.
2. Related Technology
Label printers which uses a supply of tape, housed in a cassette received in the label printer. The tape comprises an image receiving layer and a backing layer which are secured to one another via an adhesive layer. Such label printers include a cutting mechanism for cutting off a portion of the tape after an image has been printed onto the image receiving layer so that the portion of tape having the image can be used as a label. After the tape has been cut, the cut portion of the tape is pulled from the printer through a slit in the printer housing. The backing layer can then be removed allowing the image receiving layer to be secured to an object using the adhesive layer.
The label printer comprises a cassette receiving bay in which a cassette is received for printing. A print head is provided in the cassette receiving bay for co-operating with the supply of tape to print thereon. A platen may also be provided in the cassette receiving bay positioned at a side of the tape opposite to the print head when the cassette is received in the cassette receiving bay. During printing, the print head co-operates with the platen, with the tape passing therebetween for printing thereon. The platen may be driven by a motor for propagating the tape during printing. Alternatively, the platen may be freely rotatable and an additional drive roller is then provided for driving the tape during printing.
In an alternative arrangement to that described above, a platen may be provided within the cassette. In such an arrangement, the tape cooperates with a surface of the platen. When received in the cassette receiving bay the platen in the cassette co-operates with a drive mechanism in the cassette receiving bay for driving the tape during printing. Alternatively, the platen is freely rotatable and an additional drive roll is provided for driving the tape. During printing, the print head in the cassette receiving bay co-operates with the platen in the cassette with tape passing therebetween for printing thereon.
In one arrangement, the print head is movable between a non-printing position and a printing position. In an alternative arrangement, the platen is movable between a non-printing position and a printing position. In yet another arrangement, both the platen and print head are movable so as to have non-printing and printing positions.
The tape may be of a direct thermal type on which printing is achieved by direct application of heat from printing elements on the print head. Alternatively, an ink ribbon may be provided, whereby ink is transferred from the ribbon to an image receiving tape by application of heat to the ink ribbon via printing elements on the print head. The cassette may include a roll of die cut labels rather than a continuous tape.
In all the above-described arrangements, a problem exists in that for good quality printing the tape and/or ink ribbon must be correctly aligned with the print head during printing. Furthermore, the tape must remain correctly aligned with the print head while printing occurs and must smoothly pass the print head so as to ensure good quality printing, In order to ensure that this is the case, it is advantageous to prevent the cassette from moving during printing. Furthermore, the position of the cassette within the cassette receiving bay should be predefined and readily reproducable whenever a cassette is inserted in the cassette receiving bay.
In existing arrangements, this is achieved indirectly by the provision of one or more longitudinal drive shafts which project from the cassette receiving bay floor and which cooperate with one or more tape/ink ribbon spools and/or a drive roller in the cassette. Locating the cassette on these elongate members results in the cassette position being approximately in the same place whenever a cassette is placed in the cassette receiving bay. However, in such an arrangement, the height of the cassette may vary if the cassette is not fully pushed downwards into the cassette receiving bay. Furthermore, there is a certain amount of free play between the elongate members and the spools in the cassette. Accordingly, the cassette is movable by a small amount within the cassette receiving bay. This can lead to mis-alignment of the tape and print head during printing. Furthermore, if the cassette moves when printing is taking place, the tape may become creased or folded leading to poor print quality and in a worst case scenario the tape may become snagged in the mechanism which can lead to damage of the tape supply and/or the printer.
The problem is exacerbated in hand held printers which may be moved around during printing. In such an apparatus, it is even more important that the cassette is locked in a fixed position during printing.
Two types of cassette locking mechanisms are described in WO 2004/059241. In the arrangement illustrated in FIG. 11a of this document, a cassette-receiving bay is shown in which a tape cassette is inserted in a direction perpendicular to the axis of rotation of the supply spool in the cassette. The cassette-receiving bay comprises two plate like members which extend in a direction parallel to the direction of insertion of the cassette. The plate like members cooperate with opposing sides of the cassette. The plate like members are movable whereby they are moved apart to insert the cassette and then moved together to grip the cassette. A sprocket extends from one of said plate like members so as to co-operate with a spool in the tape cassette.
In an alternative arrangement illustrated in FIGS. 15 to 18c of WO 2004/059241 a locking ring mechanism and cassette are shown. In the cassette, flanges form a recess for receiving an idler roller of the printer which the emerging tape moves against as shown in FIG. 18. On the outer edge of the cassette profile are two positioning ribs and three fixation ribs. The purpose of the positioning ribs is to prevent the cassette turning in a radial direction when inserted in the printer. The purpose of the fixation ribs is to prevent axial movement of the cassette out of the printer once inserted.
The cassette receiving bay is generally circular in cross-section, with a push plate at one end and open at the other end. The cassette is inserted downwards onto the push plate. An inner side of the cassette receiving bay is formed of a locking ring. An inner surface of the locking ring has grooves for receiving the positioning ribs and fixation ribs of the cassette. A fixed part of the cassette receiving bay is disposed behind the locking ring. In order to insert the cassette, the ribs and the grooves are aligned and the cassette is pushed downwards such that each rib slides along its respective groove. The push plate is supported at its periphery by springs and is movable such that it is pushed downwards as the cassette is inserted.
The locking ring includes an exit slit for the tape so that the tape can exit the cassette-receiving bay past the idler roller. The push plate is connected to the fixed part of the cassette receiving bay and the locking ring is spring loaded in a tangential direction by a spring. As a cassette is pushed into place, the spring urges the locking ring clockwise with respect to the fixed part of the cassette-receiving bay. However the ring cannot rotate under the action of the spring until the cassette is fully inserted. This is because during insertion the fixation ribs hold the grooves open. Rotation of the locking ring locks the cassette in position. When the locking mechanism is released, the push plate urges the cassette in an upward direction ejecting the cassette from the cassette-receiving bay.